U.S. patent number 10,288,350 [Application Number 16/002,873] was granted by the patent office on 2019-05-14 for process for separating solvent from spent oil sand solids using superheated steam.
This patent grant is currently assigned to SYNCRUDE CANADA LTD.. The grantee listed for this patent is SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude Project as such owners exist now and in the future. Invention is credited to Xin Alex Wu.
United States Patent |
10,288,350 |
Wu |
May 14, 2019 |
Process for separating solvent from spent oil sand solids using
superheated steam
Abstract
A process for separating solvent from spent oil sand solids
involves drying the solids using superheated steam, and thereby
producing a vapor comprising the vaporized solvent and vaporized
water. The vapor is conveyed through a hot side of a first heat
exchanger to produce a cooled stream comprising condensed solvent
and condensed water, while a water stream is conveyed under vacuum
through a cold side of the first heat exchanger to produce steam. A
vacuum blower that applies the vacuum may also compress the steam
to adiabatically heat the steam, before the steam is further heated
by a steam superheater. The condensed water is separated from the
cooled stream, and used in producing the water stream that is
conveyed through the cold side of the heat exchanger, as the
process continues. The steam is used in producing the superheated
steam for drying the solids, as the process continues.
Inventors: |
Wu; Xin Alex (Edmonton,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude
Project as such owners exist now and in the future |
Fort McMurray |
N/A |
CA |
|
|
Assignee: |
SYNCRUDE CANADA LTD. (Fort
McMurray, CA)
|
Family
ID: |
66439477 |
Appl.
No.: |
16/002,873 |
Filed: |
June 7, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F26B
11/0477 (20130101); F26B 17/107 (20130101); F26B
25/006 (20130101); C10G 53/02 (20130101); C10G
2300/44 (20130101) |
Current International
Class: |
B01D
11/02 (20060101); F26B 17/10 (20060101); C10G
53/02 (20060101); F26B 25/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2012563 |
|
Sep 1991 |
|
CA |
|
2715301 |
|
Mar 2011 |
|
CA |
|
2724806 |
|
Jun 2011 |
|
CA |
|
2734067 |
|
Sep 2011 |
|
CA |
|
2794373 |
|
May 2014 |
|
CA |
|
2895118 |
|
Dec 2016 |
|
CA |
|
Other References
Kudra, T., et al. Superheated Steam Drying. Advanced Drying
Technologies, 2nd Edition. 2009. Chapter 7. CRC Press. pp. 89-118.
cited by applicant .
Monceaux, D.A., et al. Dryhouse Technologies and DDGS Production.
The Alcohol Textbook, 5th Edition. 2009. Chapter 21. Nottingham
University Press. pp. 303-322. cited by applicant .
Williams, M.A., et al. Recovery of Oils and Fats From Oilseeds and
Fatty Materials. Baileys Industrial Oil and Fat Products, 6th
Edition. vol. 5 Edible Oil and Fat Products: Processing
Technologies. 2005. Chapter 3. Wiley-Interscience. pp. 171-189.
cited by applicant.
|
Primary Examiner: Pregler; Sharon
Attorney, Agent or Firm: Bennett Jones LLP
Claims
The invention claimed is:
1. A process for separating solvent from spent oil sand solids
comprising the steps of: (a) drying the solids using superheated
steam, and thereby producing dried solids, and a vapor comprising
the vaporized solvent and vaporized water; (b) conveying the vapor
through a hot side of a first heat exchanger, while conveying a
water stream under vacuum through a cold side of the first heat
exchanger, thereby heating the water stream to produce steam, and
cooling the vapor to produce a first portion of uncondensed vapor,
and a first cooled stream comprising a first portion of condensed
solvent and a first portion of condensed water; (c) separating the
first portion of condensed water from the first cooled stream, and
using at least part of the separated first portion of the condensed
water in producing the water stream of step (b), as the process
continues; and (d) using a first portion of the steam in producing
the superheated steam of step (a), as the process continues.
2. The process of claim 1, wherein the cold side of the first heat
exchanger is at a pressure of less than about 70 kPa absolute.
3. The process of claim 1, wherein producing the superheated steam
comprises adiabatically compressing the first portion of the steam
to heat the first portion of the steam.
4. The process of claim 3, wherein adiabatically compressing the
first portion of the steam increases a pressure of the steam to
less than about 110 kPa absolute.
5. The process of claim 3, wherein adiabatically compressing the
first portion of the steam superheats the steam.
6. The process of claim 3, wherein the process further comprises
the step of, before conveying the vapor through the hot side of the
first heat exchanger, adiabatically compressing the vapor to heat
the vapor, wherein a temperature increase in the vapor caused by
adiabatically compressing the vapor is less than a temperature
increase in the first portion of the steam caused by adiabatically
compressing the first portion of the steam.
7. The process of claim 6, wherein adiabatically compressing the
vapor causes a temperature of the vapor to increase to less than
about 150.degree. C., and adiabatically compressing the first
portion of the steam causes a temperature of the first portion of
the steam to increase to less than about 164.degree. C.
8. The process of claim 3, wherein the process further comprises,
before conveying the vapor through the hot side of the heat
exchanger, the step of adiabatically compressing the vapor to a
pressure less than about 125 kPa absolute.
9. The process of claim 1, wherein the solids are dried in a dryer
having a vapor space at a pressure within about 1 kPa of the
ambient pressure.
10. The process of claim 9, wherein the dried solids have a
temperature of about 100.degree. C. or greater.
11. The process of claim 1, wherein the pressure of the vapor space
of the dryer is less than about 90 kPa absolute.
12. The process of claim 11, wherein the dried solids have a
temperature of about 46.degree. C. to about 97.degree. C.
13. The process of claim 1, wherein the process further comprises
the steps of conveying the dried solids and a second portion of the
steam through a sealed conduit to strip residual solvent from the
dried solids.
14. The process of claim 13, wherein the dried solids and the
second portion of the steam are conveyed in counter-current to each
other through the sealed conduit.
15. The process of claim 13, wherein the process further comprises
the steps of: (e) conveying the vapor through a baghouse to remove
fine solids from the vapor; and (f) combining the fine solids with
the dried solids after being stripped of the residual solvent.
16. The process of claim 1, wherein the process further comprises
the steps of: (e) conveying the vapor through a baghouse to remove
fine solids from the vapor; and (f) conveying a portion of the
superheated steam through the baghouse to maintain the vapor in the
baghouse at a temperature above a dew point temperature, thereby
preventing condensation of the vapor in the baghouse.
17. The process of claim 1, wherein a portion of the water stream
remains in a liquid state after being conveyed through the cold
side of the heat exchanger, and the method further comprises the
step of using the portion of the water that remains in the liquid
state in producing the water stream of step (b), as the process
continues.
18. The process of claim 1, wherein the process further comprises
the steps of: (e) conveying the first portion of uncondensed vapor
through a hot side of a second heat exchanger, thereby producing
from the first portion of the uncondensed vapor, a second portion
of uncondensed vapor, and a second cooled stream comprising a
second portion of condensed water; (f) separating the second
portion of condensed water from the second cooled stream, and using
the separated second portion of the condensed water in producing
the water stream of step (b) of claim 1, as the process continues;
(g) conveying the second portion of uncondensed vapor through a hot
side of a third heat exchanger, thereby producing from the second
portion of the uncondensed vapor, a third cooled stream comprising
a third portion of condensed water; and (h) separating the third
portion of condensed water from the third cooled stream, and using
the separated third portion of the condensed water in producing the
water stream of step (b) of claim 1, as the process continues.
19. The process of claim 18, wherein a temperature of the second
portion of condensed water is greater than a temperature of the
third portion of condensed water.
20. The process of claim 19, wherein an amount of the separated
second portion of the condensed water used in producing the water
stream of step (b) of claim 1 is greater than an amount of the
separated third portion of the condensed water used in producing
the water stream of step (b) of claim 1.
21. The process of claim 1, wherein the solvent comprises
hydrocarbons with five to twelve carbon atoms per molecule.
Description
FIELD OF THE INVENTION
The present invention relates to a process for separating
hydrocarbon solvent from spent oil sand solids after oil sand
bitumen has been extracted with the solvent. More particularly, the
present invention relates to improvements to such a process that
uses superheated steam to heat the solids, which improvements may
increase the energy efficiency of the process, and the solvent
recovery by the process.
BACKGROUND OF THE INVENTION
Solvent extraction processes that use hydrocarbon solvents to
extract bitumen from mined oil sands require little or no water,
generate no wet tailings, and can achieve higher bitumen recovery
than the existing Clark hot water extraction process or its
variants. However, they requires a process for effective separation
of solvent from the spent oil sands solids. This separated solvent
may be recycled for use in extracting bitumen as the solvent
extraction process continues. The separated oil sands solids may be
used to form trafficable solids. Typical spent oil sands solids are
in solid lump form, and contain water in the amount of about 5
weight percent, and solvent in the amount of about 5 to 10 weight
percent. The solvent trapped in the spent oil sands solids is
difficult to remove and recover.
FIG. 1 shows a flow diagram of a process for recovering solvent
from spent oil sands solids, as described in Canadian Patent No.
2,794,373 (Wu et al.). The process involves drying the solids using
superheated steam to vaporize solvent and water. The vapor is
compressed and condensed in the hot side of a first heat exchanger
to produce condensates including condensed hot water, condensed
solvent, and uncondensed vapor. The condensed hot water and
condensed solvent are separated from the uncondensed vapor in a
first separator. Hot water is flowed through the cold side of the
first heat exchanger to produce near-saturated steam. The near
saturated steam is superheated in a second heat exchanger to
produce the superheated steam for drying the solids. Uncondensed
vapor from the first separator can be further condensed in a third
heat exchanger to produce warm water, recovered solvent, and
uncondensed off gas. The uncondensed off gas can be separated in a
second separator. Some of the warm water is combined with the hot
water to produce the near-saturated steam for superheating. The off
gas is oil scrubbed or combusted prior to release to the
atmosphere.
The process described by Wu et al. can effectively recover solvents
form spent oil sands solids. However, a substantial amount of
energy is needed to produce the condensates by compressing the
vapor by a compression ratio in the range of 1.3 to 2.5.
Compression is needed to raise the dew point of the vapor above
100.degree. C. so that there is a temperature difference between
condensing vapor on the hot side and vaporizing water on the cold
side. However, compression of the vapor substantially raises the
temperature of the vapor due to the adiabatic effect. While some of
the heat in the vapor is transferred to the steam which is used in
drying the solids, excess steam production wastes energy.
Furthermore, higher vapor temperature needs to be brought down to
its dew point prior to condensation in the heat exchanger. While
the heat transfer coefficient for vapor condensation is high, the
heat transfer coefficient for gas/vapor cooling is quite low. This
increases the heat exchanging area required of the first heat
exchanger, and hence the capital cost of the heat exchanger.
Commercial application of the solvent recovery process described in
Wu et al. would benefit from improvements, including improvements
in energy efficiency. For large-scale oil sands operations
involving throughput rates on the magnitude of 8000 tonnes per hour
of mined oil sands, even incremental gains in energy efficiency can
substantially impact absolute energy consumption and operating
costs.
SUMMARY OF THE INVENTION
Improvements, as described below, are made to the process for
recovering solvent from spent oil sands solids described in
Canadian Patent No. 2,794,373 (Wu et al.). Each of the improvements
may be implemented individually, or in combination with one or more
of the other improvements.
First, when conveying vapor produced by drying the solids through
the hot side of a first heat exchanger, a vacuum is applied to the
cold side of the first heat exchanger through which a water stream
is conveyed. Consequently, the water stream forms steam at a
temperature that is lower than the temperature that would be
required to form steam in the absence of the vacuum, which is
around 100.degree. C. Therefore, the dew point of the vapor flowing
through the hot side of the first heat exchanger may not need to be
as high as in the prior art method described in Wu et al. to
achieve the same temperature difference between the condensing and
the vaporizing sides of the exchanger. This means that the vapor
does not to be compressed at all, or at least not as much as in the
prior art method described in Wu et al., before the vapor is
conveyed through the hot side of the first heat exchanger. Less
compression reduces or minimizes the increase in vapor temperature
by the adiabatic effect. This reduces or minimizes the generation
of excess steam, and the heat exchanging area required of the first
heat exchanger.
Second, the steam produced by conveying the water stream through
the cold side of the first heat exchanger may be subsequently
compressed to break the vacuum to reach near atmospheric pressure
for its reuse in the dryer. This compression increases the
temperature of the steam according to the adiabatic effect. The
compression is desirable on this side of the process since it can
be used to increase the temperature of the steam towards a
superheated condition. Therefore, less energy may be required from
a gas-fired furnace that may be used to further heat the steam
towards the superheated condition. Surprisingly, the combined
energy, likely electric energy, required to compress the vapor and
compress the steam, may be less than the energy required to
compress the vapor in the prior art method described in Wu et
al.
Third, the solids may be dried under a vacuum (i.e., under pressure
conditions that are less than atmospheric pressure). This decreases
the solids temperature at which liquid solvent and water in the
solids vaporizes to form the vapor that is flowed through the hot
side of the first heat exchanger. Accordingly, the dried solids may
be produced at a lower temperature than that produced in the prior
art process described in Wu et al., which results in less heat
energy being wasted in the dried solids.
Fourth, a portion of the steam produced by the first heat exchanger
may be used to strip residual solvent from the dried solids. This
makes use of excess steam that may be produced by the first heat
exchanger.
Fifth, a portion of the superheated steam produced by a steam
superheater may be used to heat the vapor in a cyclone/baghouse
that is used to filter fine solids from the vapor. This may help
maintain the vapor temperature in the cyclone/baghouse above its
dew point, and thereby prevent formation of condensates in the
cyclone/baghouse.
Sixth, a portion of the water stream that emerges from the cold
side of the first heat exchanger may not be converted to steam, but
may contain a substantial amount of heat. To reduce loss of heat
from this portion of the water stream, it may be recycled to the
water stream that flows through the cold side of the first heat
exchanger.
Seventh, the uncondensed vapor that emerges from the first heat
exchanger may have substantial heat energy. The uncondensed vapor
is flowed through a second heat exchanger and a third heat
exchanger to produce a second portion of condensed water, and a
third portion of condensed water, where the second and third heat
exchangers are arranged in series. The second and third portions of
condensed water may be recycled to the water stream that flows
through the cold side of the first heat exchanger to reduce loss of
heat from the uncondensed vapor. Preferably, the temperature of the
second portion of condensed water is higher than the temperature of
the third portion of condensed water. Preferably, the amount of the
second portion of condensed water that is recycled to water stream
that flows through the cold side of the first heat exchanger is
greater than the amount of the third portion of condensed water
that is recycled to water stream that flows through the cold side
of the first heat exchanger.
In one aspect, the present invention comprises a process for
separating solvent from spent oil sand solids. The process includes
the steps of: (a) drying the solids using superheated steam, and
thereby producing dried solids, and a vapor comprising the
vaporized solvent and vaporized water; (b) conveying the vapor
through a hot side of a first heat exchanger, while conveying a
water stream under vacuum through a cold side of the first heat
exchanger, thereby heating the water stream to produce steam, and
cooling the vapor to produce a first portion of uncondensed vapor,
and a first cooled stream comprising a first portion of condensed
solvent and a first portion of condensed water; (c) separating the
first portion of condensed water from the first cooled stream, and
using at least part of the separated first portion of the condensed
water in producing the water stream of step (b), as the process
continues; and (d) using a first portion of the steam in producing
the superheated steam of step (a), as the process continues.
In one embodiment of the process, the cold side of the first heat
exchanger is at a pressure of less than about 70 kPa absolute.
In one embodiment of the process, producing the superheated steam
comprises adiabatically compressing the first portion of the steam
to heat the first portion of the steam. Adiabatically compressing
the first portion of the steam may increase a pressure of the steam
to less than about 110 kPa, absolute. Adiabatically compressing the
first portion of the steam may superheat the steam.
In one embodiment of the process, the process may further comprise
the step of, before conveying the vapor through the hot side of the
first heat exchanger, adiabatically compressing the vapor to heat
the vapor, wherein a temperature increase in the vapor caused by
adiabatically compressing the vapor is less than a temperature
increase in the first portion of the steam caused by adiabatically
compressing the first portion of the steam. Adiabatically
compressing the vapor may cause a temperature of the vapor to
increase to less than about 150.degree. C., and adiabatically
compressing the first portion of the steam may cause a temperature
of the first portion of the steam to increase to less than about
164.degree. C.
In one embodiment of the process, the process further comprises,
before conveying the vapor through the hot side of the heat
exchanger, the step of adiabatically compressing the vapor to a
pressure less than about 125 kPa absolute.
In one embodiment of the process, the solids are dried in a dryer
having a vapor space at a pressure within about 1 kPa of the
ambient pressure, which may be either less than or greater than the
ambient pressure. In one embodiment, the pressure of the vapor
space is at a pressure of less than 1 kPa below the ambient
pressure. The dried solids may have a temperature of about
100.degree. C. or above. In one embodiment of the process, the
pressure of the vapor space is less than about 90 kPa absolute. The
dried solids may have a temperature of about 46.degree. C. to about
97.degree. C.
In one embodiment of the process, the process further comprises the
steps of conveying the dried solids and a second portion of the
steam through a sealed conduit to strip residual solvent from the
dried solids. The dried solids and the second portion of the steam
may be conveyed in counter-current to each other through the sealed
conduit. The process may further comprise the steps of: (a)
conveying the vapor through a baghouse to remove fine solids from
the vapor; and (b) combining the fine solids with the dried solids
after being stripped of residual solvent.
In one embodiment of the process, the process further comprises the
steps of: (a) conveying the vapor through a baghouse to remove fine
solids from the vapor; and (b) conveying a portion of the
superheated steam through the baghouse to maintain the vapor in the
baghouse at a temperature above a dew point temperature, thereby
preventing condensation of the vapor in the baghouse.
In one embodiment of the process, a portion of the water stream
remains in a liquid state after being conveyed through the cold
side of the heat exchanger, and the method further comprises the
step of using the portion of the water that remains in the liquid
state in producing the water stream of step (b), as the process
continues.
In one embodiment of the process, the process further comprises the
steps of: (a) conveying the first portion of uncondensed vapor
through a hot side of a second heat exchanger, thereby producing
from the first portion of the uncondensed vapor, a second portion
of uncondensed vapor, and a second cooled stream comprising a
second portion of condensed water; and (b) separating the second
portion of condensed water from the second cooled stream, and using
the separated second portion of the condensed water in producing
the water stream of step (b) of claim 1, as the process continues;
(c) conveying the second portion of uncondensed vapor through a hot
side of a third heat exchanger, thereby producing from the second
portion of the uncondensed vapor, a third cooled stream comprising
a third portion of condensed water; and (d) separating the third
portion of condensed water from the third cooled stream, and using
the separated third portion of the condensed water in producing the
water stream of step (b) of claim 1, as the process continues.
A temperature of the second portion of condensed water may be
greater than a temperature of the third portion of condensed water.
An amount of the separated second portion of the condensed water
used in producing the water stream of step (b) of the process, as
first described above, is greater than an amount of the separated
third portion of the condensed water used in producing the water
stream of step (b) of the process, as first described above.
In an embodiment of the process, the solvent comprises hydrocarbons
with five to twelve carbon atoms per molecule.
In another aspect, the present invention comprises a system for
recovering solvent from spent oil sand solids. The system
comprises: (a) a dryer comprising a dryer solids inlet, a dryer
superheated steam inlet, and a dryer vapor outlet; (b) a first flow
path comprising the following elements in sequential fluid
communication: (i) the dryer vapor outlet; (ii) a hot side of a
first heat exchanger; and (iii) a first separator comprising a
first separator water outlet; and (c) a second flow path comprising
the following elements in sequential fluid communication: the first
separator water outlet; (ii) the cold side of the first heat
exchanger; (iii) a vacuum blower for applying a vacuum to the cold
side of the first heat exchanger, and adiabatically compressing
steam exiting from the cold side of the first heat exchanger; (iv)
a steam superheater; and (v) the dryer superheated steam inlet.
In one embodiment of the system, the system further comprises a
blower for adiabatically compressing vapor exiting the dryer vapor
outlet, wherein the blower is operable to adiabatically compress
vapor exiting the dryer vapor outlet to cause an increase in the
temperature of the vapor, wherein the vacuum blower is operable to
adiabatically compress steam exiting from the cold side of the
first heat exchanger to cause an increase in the temperature of the
steam, wherein the increase in the temperature of the steam is
greater than the increase in the temperature of the vapor.
In one embodiment of the system, the dryer comprises a dryer solids
outlet with an air-lock device for maintaining a vapor space in the
dryer under vacuum.
In one embodiment of the system, the system further comprises a
sealed conduit for conveying dried solids from the dryer, and
conveying steam from the cold side of the first heat exchanger in
counter-current to the dried solids in the sealed conduit.
In one embodiment of the system, the system further comprises a
baghouse for filtering fine solids from vapor exiting the dryer
vapor outlet, a baghouse vapor outlet in communication with the hot
side of the first heat exchanger, and a baghouse fine solids outlet
in communication with the sealed conduit.
In one embodiment of the system, the system further comprises a
baghouse for filtering fine solids from vapor exiting the dryer
vapor outlet, and a conduit for conveying superheated steam exiting
the steam superheater to the baghouse.
In one embodiment of the system, the system further comprises a
conduit for recycling water from an outlet of the cold side of the
heat exchanger to an inlet of the cold side of the heat
exchanger.
In one embodiment of the system, the first separator further
comprises a first separator vapor outlet, and the system further
comprises: (a) a third flow path comprising the following elements
in sequential fluid communication: (i) the first separator vapor
outlet; (ii) a hot side of a second heat exchanger; and (iii) a
second separator comprising a second separator water outlet, and a
second separator vapor outlet; and (b) a fourth flow path
comprising the following elements in sequential fluid
communication: (i) the second separator vapor outlet; (ii) a hot
side of a third heat exchanger; and (iii) a third separator
comprising a third separator water outlet, wherein the second
separator water outlet and the third separator water outlet are in
fluid communication with the second flow path upstream of the cold
side of the first heat exchanger.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings shown in the specification, like elements may be
assigned like reference numerals. The drawings are not necessarily
to scale, with the emphasis instead placed upon the principles of
the present invention. Additionally, each of the embodiments
depicted are but one of a number of possible arrangements utilizing
the fundamental concepts of the present invention.
FIG. 1 is a schematic flow diagram of one embodiment of a prior art
process for recovering solvent from spent oil sands solids, as
described in Canadian Patent No. 2,794,373 (Wu et al.).
FIG. 2 is a schematic flow diagram of one embodiment of a process
of the present invention for recovering solvent from spent oil
sands solids.
FIG. 3 shows a table summarizing mass flow rates of water (H.sub.2O
rate) and solvent (C.sub.6-C.sub.9 rate), temperature (T), and
pressure (P) in various streams of the prior art process shown in
FIG. 1, and the process of the present invention shown in FIG. 2,
as predicted by a chemical process simulation.
FIG. 4 shows a chart of temperature (T) versus molar volume
(V.sub.m) for water/steam as the heating medium as it proceeds
through the prior art process shown in FIG. 1 (dashed line) and the
process of the present invention shown in FIG. 2 (solid line), as
predicted by a chemical process simulation.
FIG. 5 shows a table summarizing natural gas consumption and
electricity consumption of an example of a modified version of the
prior art process shown in FIG. 1, and an example of the process of
the present invention shown in FIG. 2, as predicted by a chemical
process simulation.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The present invention relates generally to a process of recovering
solvent from spent oil sand solids using superheated steam. The
invention is particularly useful for recovering solvent having five
to twelve carbon atoms per molecule or mixtures thereof including,
but not limited to, pentane, hexane, heptane, octane, and nonane.
For solvent having ten to twelve carbon atoms per molecule, the
process may not completely recovery the solvent, but can be used to
partially recover the solvent.
FIG. 2 is a flow diagram of the process of the present invention.
In FIG. 2, elements that are equivalent to the elements shown in
FIG. 1 are assigned common reference numerals. Moreover, elements
that are shown in dashed line in FIG. 2 indicate elements that are
not shown in FIG. 1. The conduits among the various components may
be constructed from any suitable piping as is employed in the art.
Suitable piping includes, without limitation, plastic piping,
galvanized metal piping, and stainless steel piping. In one
embodiment, some of the conduits may comprise a screw conveyor or
auger conveyor.
Referring to FIG. 2, wet spent oil sand solids 10 are fed into a
dryer 12. In one embodiment, the dryer 12 is a direct dryer
comprising a horizontal rotary drum having flights for lifting and
cascading down solids. In one embodiment, the dryer 12 comprises a
rotary drum with a diameter of about 6 m and a length of about 12
m.
The heat for the dryer 12 is provided by superheated steam 14. As
used herein, the term "superheated steam" means steam at a
temperature higher than water's boiling point at the same pressure.
In one embodiment, the temperature of the superheated steam 14
ranges from 400.degree. C. to 900.degree. C. In one embodiment, the
pressure of the superheated steam 14 fed to the dryer 12 and the
pressure in the vapor space of the dryer 12 are both near ambient
pressure (i.e, within about 1 kPa of the ambient pressure, which
may be either greater than or less than the ambient pressure). In
one embodiment, the pressure in the vapor space of the dryer 12 is
less than 1 kPa below ambient pressure to prevent leakage of
solvent vapor from the dryer 12. In another embodiment, the
pressure of the superheated steam 14 and the pressure in the vapor
space of the dryer 12 are both significantly below ambient
pressure, in the range of 10 to 90 kPa absolute. As used herein
"absolute" pressure means pressure measured in reference to a
perfect vacuum. This makes water and solvents vaporize at about 3
to 54.degree. C. lower than the temperature required in the case of
the vapor space in the dryer 12 being near ambient pressure. In
such embodiments, the wet solids stream 10 must be fed through an
airlock-like device to maintain vacuum in the dryer 12.
The superheated steam 14 flow rate is set to a value which does not
cause excessive dust carryover and premature solids removal prior
to sufficient drying. Variation in feed moisture content is handled
by adjusting the temperature of the superheated steam 14 to
maintain the temperature of the resulting dry solids 13 at or above
100.degree. C. when the vapor pressure in the dryer 12 is near
ambient pressure, and at about 46 to 97.degree. C. when the
pressure in the dryer 12 is significantly below ambient pressure.
Since the heat in dry solids 13 is mostly wasted, reducing the
temperature of the dry solids 13 is beneficial from an energy
efficiency standpoint. In one embodiment, the temperature of the
vapor 18 produced by the dryer 12 is about 20.degree. C. higher
than the temperature of the dry solids 13 regardless of the dryer
pressure. In the case where pressure in the vapor space of the
dryer 12 is near ambient dryer pressure, the temperature of the
exiting vapor 18 is always above 100.degree. C. In one embodiment,
the temperature of the vapor 18 is about 120.degree. C.
The vapor 18 exits the dryer 12 through an insulated duct and is
cleaned through a cyclone, baghouse, or both 20. The pressure in
the cyclone/baghouse 20 is similar to that in the dryer 12. The
cyclone of the cyclone/baghouse 20 creates a vortex to separate any
fine solids 22 from the vapor 18. The baghouse of the
cyclone/baghouse 20 is a collector in which fine solids 22 are
removed from the vapor 18 by passing the vapor 18 through a fabric
filter. The fine solids 22 are discharged and combined with the dry
solids 13 to form combined dry solids 16 for transport to a
disposal site. The combined dry solids 16 may be suitably treated
to form trafficable solids before disposal (see for example,
Canadian Patent no. 2,895,118 to Wu et al.). In one embodiment, the
dry solids 13 go through a sealed screw conveyor 102 for the
transportation. In one embodiment, a stream of slightly superheated
steam 104, which may be a slip stream of steam 44, flows
countercurrent to the dry solids 13 in the screw conveyor 102 to
further strip residual solvents in the dry solids 13. The spent
steam flows into dryer 12 and joins the dryer vapor 18. In one
embodiment, fine solids 22 join the dry solids 13 after the
countercurrent steam stripping to minimize dust carryover, and form
the combined dry solids 16. The combined dry solids 16 must go
through an airlock-like device to reach the atmosphere from an
inert environment. In the case of dryer pressure significantly
below ambient pressure, the airlock-like device also helps in
maintaining a vacuum in the dryer 12.
The cyclone/baghouse 20 produces filtered vapor 24, which enters a
blower or a compressor 26 which increases the pressure of the
filtered vapor 24 by reducing their volume and producing compressed
vapor 28. In the case where vapor pressure in the dryer 12 is near
ambient pressure, the compression ratio is in the range of 1.0 to
1.5. In one embodiment, the compression ratio is about 1.3, and
raises the pressure of the filtered vapor 24 from about 95 kPa to
about 122 kPa absolute. In the case where vapor pressure in the
dryer 12 is significantly below ambient pressure, the compression
ratio is higher to raise the pressure of the filtered vapor 24 to
the same level as the case where the vapor pressure in the dryer 12
is near ambient pressure. In one embodiment, the compressed vapor
28 is at about 122 kPa absolute regardless of the dryer pressure.
Thus, the dew point of the compressed vapor 28 is about 105.degree.
C.
The compressed vapor 28 enters a heat exchanger 30. The heat
exchanger 30 and all heat exchangers described herein may comprise
any suitable single heat exchanger or multiple-stage heat
exchangers and may be constructed from any suitable materials
including copper and aluminum. In one embodiment, the heat
exchanger 30 comprises multiple falling film evaporators. The
compressed vapor 28 enters through the hot side of the heat
exchanger 30 for cooling and condensation. As used herein, the term
"condensation" means the change of the physical state of matter
from the gaseous phase into the liquid phase, and is the reverse of
vaporization. Condensation occurs when a vapor is cooled and/or
compressed to its saturation limit when the molecular density in
the gas phase reaches its maximum threshold.
The heat exchanger 30 produces a cooled stream 32 comprising
condensates (water and liquid solvent) and uncondensed vapor. The
cooled stream 32 is transferred from the heat exchanger 30 to a
separator 34. In one embodiment, the separator 34 comprises a
3-phase separator. As used herein, the term "3-phase separator"
means a vessel capable of separating water, liquid hydrocarbon, and
gases in a process stream. The 3-phase separator may be horizontal
or vertical.
Hot water 36 having a temperature ranging from 90.degree. C. to
100.degree. C. exits the separator 34, and combines with two hot
water streams 106 and 108 to produce a stream of combined water 38.
In one embodiment, the hot water 36 has a temperature of about
94.degree. C. In one embodiment, the hot water 106 and 108 have
temperatures of about 91.degree. C. and about 88.degree. C.,
respectively. In one embodiment, hot water 36 further combines with
a warm water stream 68 to produce the combined water 38. In one
embodiment, the warm water 68 has a temperature of about 60.degree.
C. In one embodiment, the combined water 38 has a temperature of
about 92.degree. C.
The combined water 38 enters through the cold side of the heat
exchanger 30. Hot water that is not evaporated in the heat
exchanger 30 is separated and recycled through water stream 108 to
the combined water 38. In one embodiment, part of the stream 108 is
purged and disposed to prevent accumulation of contaminants such as
fine solids.
Pressure is reduced in the conduit carrying the combined water 38
by means of a vacuum blower 110 downstream of the heat exchanger
30. In one embodiment, the vacuum blower 110 can be any mechanical
device that generates vacuum. In one embodiment, the pressure in
the conduit that carries the combined water 38 is about 70 kPa
absolute. The combined water 38 boils at about 90.degree. C. to
form saturated steam 40. As used herein, "saturated steam" means
steam which is in equilibrium with heated water at the same
pressure, i.e., it has not been heated past the boiling point for
that pressure.
The liquid water-free saturated steam 40 enters the vacuum blower
110. In one embodiment, the steam 40 has a temperature of
88.degree. C. and a pressure of 60 kPa absolute. After compression
in the vacuum blower 110, the pressure of steam 112 increases to be
slightly above the ambient pressure. In one embodiment, the steam
112 has a pressure of 110 kPa absolute and a temperature of
164.degree. C. This makes the steam 112 slightly superheated.
A portion of the slightly superheated steam 112 is diverted to
stream 44 for use in other processes such as, for example, solvent
or water-based extraction. The majority of steam 112 follows
conduit 74 and enters a heat exchanger, hereinafter referred to as
a steam superheater 42. A furnace 46 generates a hot combustion gas
stream 48 which enters the steam superheater 42 to superheat the
steam 112. The cooled flue gas 50 exits the steam superheater 42.
The superheated steam 43 generated in the steam superheater 42 is
directed to the dryer 12. In one embodiment, the steam superheater
42 is a gas-gas heat exchanger. In another embodiment, the steam
superheater 42 comprises heat exchanging surfaces built within the
furnace 46. In one embodiment, a slip stream of superheated steam
100 is split from the main conduit of superheated steam 43 to the
cyclone/baghouse 20 to increase the vapor temperature in there to
about 130.degree. C. This prevents condensation in the
cyclone/baghouse 20. Downstream of the split, the superheated steam
becomes stream 14.
The separator 34 also generates recovered solvent 52 and
uncondensed vapor 54. In one embodiment, the pressure of vapor 54
is near ambient pressure. In one embodiment, a stream of
uncondensed vapor is diverted via conduit 114 to a compressor or
blower 116. The blower 116 slightly increases the pressure of the
recovered vapor to overcome the friction losses in the downstream
units. After the blower 116, the uncondensed vapor 118 enters a
heat exchanger 120. In one embodiment, the heat exchanger 120
includes heating jackets and/or heating tubes in solvent or
water-based extraction. After partial vapor condensation, the
mixture 122 enters a separator 124. In one embodiment, the
separator 124 comprises a 3-phase separator wherein the condensed
hot water stream 106, recovered solvent 126 and uncondensed vapor
128 are separated. The hot water 106 is recycled in the combined
water 38. The uncondensed vapor 128 is returned to the conduit that
carries the uncondensed vapor 54.
The vapor 54 flows into a blower or compressor 130 to slightly
increase the pressure to overcome the friction losses in the
downstream units. After the blower 130, the vapor 132 enters a heat
exchanger 56 for cooling and condensation mediated by cooling water
58 which flows through the heat exchanger 56. The cooled stream 60
flows into a separator 62. In one embodiment, the cooled stream 60
has a temperature of about 60.degree. C. In one embodiment, the
separator 62 comprises a 3-phase separator. The separator 62
separates warm water 68, recovered solvent 64, and off gas 66 from
the cooled stream 60. In one embodiment, a portion of the warm
water 68 is recycled to the combined water 38. The remainder of the
warm water 70 is disposed or recycled in other processes such as,
for example solvent or water-based extraction. The temperature for
the cooled stream 60 may be lower if more volatile hydrocarbon
solvents are present. The off gas 66 may be scrubbed in an oil
scrubber to further remove solvent vapor before being released to
the atmosphere or being combusted. Alternately, the off gas 66 may
be combusted without oil scrubbing.
The multi-stage cooling and condensation process involving use of
the heat exchanger 30, the separator 34, the heat exchanger 120,
and the separator 124 conserves energy by recycling the combined
hot water 38 near its boiling point at reduced pressure. The last
cooling and condensation step involving use of the heat exchanger
56 and the separator 62 achieves high solvent recovery by cooling
the vapor 132 to a lower temperature in the heat exchanger 56. In
one embodiment, the solvent recovery in the process is above 98%.
The lost solvent is mainly in the off gas 66, which is combusted or
scrubbed and recovered. Only a trace amount of solvent is lost to
the atmosphere in the combined dry solids 16.
Example.
Exemplary embodiments of the present invention are described in the
following examples, which are set forth to aid in the understanding
of the invention, and should not be construed to limit in any way
the scope of the invention as defined in the claims which follow
thereafter.
A modified version of the prior-art process shown in FIG. 1 and the
process shown in FIG. 2 were simulated using Aspen HYSYS.TM. v8.4
2013 (AspenTech, Burlington, Mass.), a chemical process simulation
software. The process of FIG. 1 was modified to include a blower
110 (analogous to that shown in FIG. 2) because the blower may
practically be needed to compress the steam in conduit 74 upstream
of the steam superheater 42 to overcome the pressure loss in steam
superheater 42. A feed rate of wet solids 10 of 554 metric tonnes
per hour (t/h) at 45.degree. C. was assumed in the simulation. The
wet solids 10 contained 5.7 weight % water (31.5 t/h) and 10.6
weight % solvent (58.8 t/h). The solvent was assumed to be a light
naphtha cut (i.e., a mixture of hydrocarbon molecules having six to
nine carbon atoms) with a boiling range of 73 to 168.degree. C. It
was further assumed that 28.7 t/h water and 58.8 t/h solvent were
vaporized in a rotary dryer 12 that has a diameter of 6 m and a
length of 12 m. The velocity of the vapor stream flowing through
the cross-section of the dryer 12 was kept at 3 m/s. The air leak
and/or nitrogen purge rate into the dryer 12 was assumed to be 0.36
t/h.
FIG. 3 shows a table that summarizes the simulation results for
mass flow rates of water (H.sub.20) and solvent (C.sub.7),
temperature (T), and pressure (P) in streams of the prior art
process shown in FIG. 1 (denoted "FIG. 1"), and the process of the
present invention in FIG. 2 (denoted "FIG. 2"), as predicted by the
Aspen HYSYS.TM. simulation.
FIG. 4 shows a chart of temperature (T) versus molar volume
(V.sub.m) for water/steam as the heating medium as it proceeds
through the prior art process shown in FIG. 1 (dashed line) and the
process of the present invention shown in FIG. 2 (solid line), as
predicted by the Aspen HYSYS.TM. simulation. Each dot represents
the state of a stream. The stream numbers are shown beside the
dots, with stream numbers for the process of FIG. 1 shown in
parentheses.
FIG. 5 shows a table that summarizes the natural gas and
electricity consumption of the prior art process shown in FIG. 1
(denoted "FIG. 1"), and the process of the present invention in
FIG. 2 (denoted "FIG. 2"), as predicted by the Aspen HYSYS.TM.
simulation.
Based on FIGS. 3 to 5, the following observations may be made.
First, for the process of FIG. 2 in comparison to the process of
FIG. 1, there is a significant reduction of temperature (33.degree.
C.) of stream 28 prior to vapor condensation by the heat exchanger
30. It is unexpected that, by evaporating the water under vacuum on
the cold side of the heat exchanger 30, the vapor 24 on the hot
side of the heat exchanger 30 needs little or no compression, while
still maintaining a temperature difference of 15.degree. C. between
the two sides of the exchanger that is sufficient for proper heat
exchange. With moderate or no compression of the vapor 24, the
increase in the temperature of the vapor 24 due to the adiabatic
compression is not as significant. For example, in the prior art
process of FIG. 1, the compressor 26 compresses the vapor 24 to
vapor 28 with a pressure increase of 76 kPa, and a temperature
increase of 56.degree. C. In contrast, in the process of FIG. 2,
the compressor 26 compresses the vapor 24 to vapor 28 with a
pressure increase of only 27 kPa, and a temperature increase of
only 23.degree. C. Thus, the lower temperature of vapor 28 helps in
reducing the waste heat in form of surplus steam 44. Further, a
lower temperature of vapor 28 is advantageous over a higher
temperature of vapor 28 since the vapor 28 needs to be cooled to
its dew point before it transfers significant heat. Therefore, the
lower temperature of vapor 28 also reduces the heat exchanging duty
of a cooling vapor prior to condensation. Because of low heat
transfer coefficient for gas/vapor cooling, this reduction of heat
exchanging duty improves the efficiency and reduces the required
surface area of the heat exchanger 30 for the process of FIG.
2.
Second, for the process of FIG. 2 in comparison to the process of
FIG. 1, there is a significant increase of temperature (41.degree.
C.) of the stream in conduit 74 prior to steam superheating by the
steam superheater 42. This is also beneficial to the process
efficiency since less energy input is required for the steam
superheater 42 to produce the superheated steam 14, which is used
to heat wet solids 10.
Third, for the process of FIG. 2 in comparison to the process of
FIG. 1, electricity consumption is reduced by about 2.7%. It is
surprising that to keep the same dew point difference of 15.degree.
C. between the hot and the cold sides of the heat exchanger 30 (in
the process of FIG. 1, 115.degree. C.-100.degree. C.=15.degree. C.;
and in the process of FIG. 2, 105.degree. C.-90.degree. C.) when
condensation and vaporization occur on both sides, the total
electricity input in the process of FIG. 2 is less than the total
electricity input in the process of FIG. 1.
Fourth, for the process of FIG. 2 in comparison to the process of
FIG. 1, natural gas consumption is reduced by about 5.9%. In the
process of FIG. 1, the main electricity input is to the blower 26
on the hot side of the heat exchanger 30. In contrast, in the
process of FIG. 2, the main electricity input is to the vacuum
blower 110 on the cold side of the heat exchanger 30. By using most
of the electric energy on the cold side of the heat exchanger 30,
the temperature of the newly generated steam 40 increases
significantly on account of the adiabatic compression principle of
thermodynamics. In the prior art process of FIG. 1, the steam from
stream 40 to 74 increases in temperature by only 25.degree. C.
(from 98.degree. C. to 123.degree. C.). In contrast, in the process
of FIG. 2, the steam from stream 40 to 74 increases in temperature
by 76.degree. C. (from 88.degree. C. to 164.degree. C.). Since this
steam 40 is to be superheated by means of natural gas combustion in
the furnace 46, preheating the steam 40 with the compression work
of the vacuum blower 110 significantly reduces the amount of
natural gas consumed by the furnace 46. It is surprising that this
results in even more energy savings than the aforementioned
reduction of electricity input.
In summary, adding the vacuum blower 110 to the prior art process
of FIG. 1, decreases the total electricity and natural gas
consumptions, reduces the amount of waste heat, and improves the
heat transfer efficiency of the heat exchanger 30.
Fifth, for both processes, the solvent recovery from the cooled
stream 32 of vapor condensed by the heat exchanger 30 is more than
99% (i.e., the C.sub.6-C.sub.9 Rate of 58.6 t/h of cooled stream
32, divided by the C.sub.6-C.sub.9 Rate of 58.8 t/h of the wet
spent oil sand solids 10) if an oil scrubber (not shown) is added
for the off-gas (stream 66).
References.
The following references are incorporated herein by reference
(where permitted) as if reproduced in their entirety. All
references are indicative of the level of skill of those skilled in
the art to which this invention pertains. Canadian Patent No.
2,794,373 (Wu et al.). Canadian Patent No. 2,895,118 (Wu et
al.)
Interpretation.
The detailed description set forth above in connection with the
appended drawings is intended as a description of various
embodiments of the present invention and is not intended to
represent the only embodiments contemplated by the inventor. The
detailed description includes specific details for the purpose of
providing a comprehensive understanding of the present invention.
However, it will be apparent to those skilled in the art that the
present invention may be practiced without these specific
details.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and
without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions. Thus, the present invention is not
intended to be limited to the embodiments shown herein, but is to
be accorded the full scope consistent with the claims, wherein
reference to an element in the singular, such as by use of the
article "a" or "an" is not intended to mean "one and only one"
unless specifically so stated, but rather "one or more". All
structural and functional equivalents to the elements of the
various embodiments described throughout the disclosure that are
known or later come to be known to those of ordinary skill in the
art are intended to be encompassed by the elements of the claims.
Moreover, nothing disclosed herein is intended to be dedicated to
the public regardless of whether such disclosure is explicitly
recited in the claims.
The corresponding structures, materials, acts, and equivalents of
all means or steps plus function elements in the claims appended to
this specification are intended to include any structure, material,
or act for performing the function in combination with other
claimed elements as specifically claimed.
References in the specification to "one embodiment", "an
embodiment", etc., indicate that the embodiment described may
include a particular aspect, feature, structure, or characteristic,
but not every embodiment necessarily includes that aspect, feature,
structure, or characteristic. Moreover, such phrases may, but do
not necessarily, refer to the same embodiment referred to in other
portions of the specification. Further, when a particular aspect,
feature, structure, or characteristic is described in connection
with an embodiment, it is within the knowledge of one skilled in
the art to affect or connect such module, aspect, feature,
structure, or characteristic with other embodiments, whether or not
explicitly described. In other words, any module, element or
feature may be combined with any other element or feature in
different embodiments, unless there is an obvious or inherent
incompatibility, or it is specifically excluded.
It is further noted that the claims may be drafted to exclude any
optional element. As such, this statement is intended to serve as
antecedent basis for the use of exclusive terminology, such as
"solely," "only," and the like, in connection with the recitation
of claim elements or use of a "negative" limitation. The terms
"preferably," "preferred," "prefer," "optionally," "may," and
similar terms are used to indicate that an item, condition or step
being referred to is an optional (not required) feature of the
invention.
The singular forms "a," "an," and "the" include the plural
reference unless the context clearly dictates otherwise. The term
"and/or" means any one of the items, any combination of the items,
or all of the items with which this term is associated. The phrase
"one or more" is readily understood by one of skill in the art,
particularly when read in context of its usage.
The term "about" can refer to a variation of .+-.5%, .+-.10%,
.+-.20%, or .+-.25% of the value specified. For example, "about 50"
percent can in some embodiments carry a variation from 45 to 55
percent. For integer ranges, the term "about" can include one or
two integers greater than and/or less than a recited integer at
each end of the range. Unless indicated otherwise herein, the term
"about" is intended to include values and ranges proximate to the
recited range that are equivalent in terms of the functionality of
the composition, or the embodiment.
As will be understood by one skilled in the art, for any and all
purposes, particularly in terms of providing a written description,
all ranges recited herein also encompass any and all possible
sub-ranges and combinations of sub-ranges thereof, as well as the
individual values making up the range, particularly integer values.
A recited range includes each specific value, integer, decimal, or
identity within the range. Any listed range can be easily
recognized as sufficiently describing and enabling the same range
being broken down into at least equal halves, thirds, quarters,
fifths, or tenths. As a non-limiting example, each range discussed
herein can be readily broken down into a lower third, middle third
and upper third, etc.
As will also be understood by one skilled in the art, all language
such as "up to", "at least", "greater than", "less than", "more
than", "or more", and the like, include the number recited and such
terms refer to ranges that can be subsequently broken down into
sub-ranges as discussed above. In the same manner, all ratios
recited herein also include all sub-ratios falling within the
broader ratio.
* * * * *